First plant group: non-vascular bryophytes (mosses)

  • Mosses, hornworts and liverworts
    • Fossils of bryophyte spores ~470mya


  • Non-vascular; ground hugging carpets
    • bodies to thin to support height growth


  • Have a rhizoid but not a root
    • anchors plant
    • does not uptake water
    • need to live near water


  • Gametophyte dominated life cycle
    • sperm needs water to swim to egg on gametophyte

Vascular plants were the next evolutionary step…Why?

Vascular tissues: tissues for conducting nutrients and fluid internally

The big picture: Vascular plants now dominate Earth


  • Bryophytes ruled for <100 million years
    • vascular plants show up ~425mya


  • Plants then evolved vascular tissues
    • grow taller than bryophytes
    • tissues connected leaves to roots


  • First vascular plants lacked seeds
    • sperm also need water to swim
    • ferns and lycophytes = 1st groups


  • Fern and lycophyte diversity now diminished

Ancient seedless forests now power our planet: Coal!

Vascular system: the basics (add to phylogeny)


Xylem = water conducting cells (one way)
Phloem = sugar sap conducting cells (multi-directional)


  • Conducting cells provide biomechanical support
    • lignin in cell walls
    • does not rot easily
    • does not collapse easily
    • ‘think’ bundles of rigid pipes
    • allows plant to grow vertically


  • Vascular elements move liquid under tension


  • Vascular elements evolved independently several times

Evolution of roots (add to phylogeny)


  • Vascular tissues belowground
    • extension of ancient stems
    • bryophytes have no ‘true’ roots


  • Absorb water and nutrients
    • active explorers of soil
    • often connected with fungi


  • Anchor the plant in place
    • support vertical growth


  • Fossils show roots in lycophytes ~ 400mya
    • convergent evolution in ferns

Evolution of leaves (add to phylogeny)



  • Photosynthetic organ on plants
    • shape maximizes surface area


  • Microphylls: single unbranched vein
    • unique to lycophytes (add to phylogeny)


  • Megaphylls: leaves with many branched veins
    • majority of vascular plants (add to phylogeny)


  • Why do more veins matter?

Evolution of leaves: sporophylls (#3 on Mastering AoG)

  • Sporophyll: modified leaf with sporangium
    • vastly different looks
    • Trophophyll: vegetative leaf


  • Sporagnium: spore container (house)
    • ferns: clusters of sporagnia called ‘sori’
    • lycophytes: ‘stobilus’ holds many sporagnia (like a cone)
    • angiosperms: structures inside flowers


  • Spore mother cell: cell inside sporagnium
    • undergoes meiosis to make spores


  • What is the ploidy of each cell type in this picture?

Lycophytes: First vascular plants



  • Independent, branched sporophyte


  • Lignified vascular tissue, tracheids & roots
    • tracheid = special xylem cell


  • Leaves are microphylls
    • some with strobili (evolved multiple times)


  • Some with heterospory (Selaginella)
    • male (micro-) and female (mega-) spores

Ferns


  • Whisk Ferns, Equisetum & Ferns
    • mostly homosporous


  • Homospory = spores that germinate to produce bisexual (both male and female) gametophytes


  • Leaves are mostly megaphylls
    • whisk ferns lost leaves
    • Equistem has reduced megaphylls (tiny leaves)

Ferns


  • Whisk Ferns, Equisetum & Ferns
    • mostly homosporous
    • whisk ferns do not have roots


  • Leaves are mostly megaphylls
    • whisk ferns lost leaves
    • Equistem has reduced megaphylls (tiny leaves)


  • New Gaga genus with 19 species
    • “We wanted to name this genus for Lady Gaga because of her fervent defense of equality and individual expression” Pryer @ Duke University

Seedless vascular plants have free living separate generations


  • Sporophyte: The fern you see in the woods
    • dominant stage


  • Gametophye: independent haploid generation
    • start out female or bisexual


  • Dependent embryo (2N) develops and replaces gametophyte
    • in moss, sporophyte developers and disappears on the living gametophyte


  • What does natural selection favor diploid dominant lifecycles?

Homosphorous life cycle (mostly) with dominant sporophytes

Same AOG drawing, sporophytes are larger and long lived, gametophytes are smaller and short lived

The consequences of homospory




  • One spore → one gametophyte → bisexual gametophyte
    • everything is haploid (1N)


  • Produces both sperm and egg via mitosis


  • A lot of self fertilization
    • What is good/bad about this?

How spore-bearing plants avoid self-fertilization…


  • Fastest developing gametophyte (female) releases chemical hormone


  • Hormone turns other developing gametophytes all male
    • sperm from everywhere!
    • female power - makes her own boyfriends


  • Archegonia (F) and Antheridia (M) also mature at different times
    • if fertilization doesnt happen gametophyte becomes bisexual